As a bearing mechanism for a rotor in a vacuum pump such as a turbo-molecular pump, there is one having a structure that uses a permanent magnet and a ball bearing. The rotational frequency of a rotor of a turbo-molecular pump is higher than the resonant frequency (the secondary critical speed) of a rotor body. Therefore, it is necessary to allow the rotational frequency of the rotor to pass through the resonant frequency (critical speed) when starting and stopping the pump. Therefore, a vibration control mechanism for damping the transmission of vibration caused by resonance of the rotor to a housing is required in the turbo-molecular pump.
A typical vibration control mechanism in a structure that uses a permanent magnet and a ball bearing is illustrated in FIG. 1 of Patent Document 1. In this structure, in order to damp the movement in the radial direction of a ball bearing which is attached to a rotor shaft, a radial-direction damping elastomer ring is interposed between the outer peripheral surface of an outer peripheral ring of the ball bearing and a housing section. Further, in order to damp the movement in the axial direction of the ball bearing, an axial-direction damping elastomer ring is interposed between the end surface of the outer peripheral ring of the ball bearing and the housing.